This project aims to define how polymicrobial infection impacts the development, severity, and treatment of bacterial otitis media. Haemophilus influenzae (Hi) is the leading bacterial species associated with otitis media, and our data show that coinfection with multiple strains of Hi is common. We hypothesize that strains of Hi undergo intrastrain and interstrain quorum signaling and horizontal gene transfer within biofilm communities which impacts strain diversity and horizontal dissemination of virulence determinants. In order to address these hypotheses we will complete the following Specific Aims: Specific Aim 1. To understand relationships between Hi strains with differing production and/or sensing of quorum signal Specific Aim 2. To ask how different inters train relationships affect bacterial persistence and disease severity in the chinchilla infection model Specific Aim 3. To define emergence and dissemination of virulence determinants among Hi strains within the same biofilm community. Otitis media is among the most common pediatric infectious diseases, affecting the majority of children and accounting for billions of dollars in ttal health-care costs per year. It is clear that a significant proportion of these infections are cause by Hi, for which there is no currently licensed vaccine. Unfortunately, our ability to treat these infections is increasingly limited by the continued emergence of antibiotic-resistant bacterial strains. The results of these studies will provide significant insight into how different Hi strain act competitively and/or cooperatively during infection. Moreover, we will gain significant new information regarding how new genotypes emerge and are disseminated within a biofilm community. These findings will be crucial steps in gaining the deep understanding of basic mechanisms for persistence and virulence that will be necessary for tailoring new strategies for diagnosis, prevention, and/or therapy of otitis media infections.